see the common pattern "widget"(which help us to get form properties inside a field from a node form alter...)

And notice "subform" which go deeper to paragraphs! repeats over and over till get the field.

Once identified the field we need to use "#ajax" property and we need to pass callback which will be a function which will be declared on the .module

notice as well we use #suffix with span class="airpack-type-image" where we are going to insert image.

Now comes the tricky part! we need to get field value!

according to documentation says:

string|array $key: Values are stored as a multi-dimensional associative array. If $key is a string, it will return $values[$key]. If $key is an array, each element of the array will be used as a nested key. If $key = array('foo', 'bar') it will return $values['foo']['bar’].

Not so clear, right?

well first we need to do a dpm($form['field_aerial_detail']['widget'][0]['subform']['field_aerdet_package']['widget'][0]['subform']['field_aerpack_type']['widget']) to debug data and you'll see #parents